Quenching autofluorescence

Dear Colleagues,
I am trying to colocalize two antigens using two different fluorochromes on
Rat frozen brain sections. There is no problem with immunohistochemistry.
Except that there are little particles on the tissue that autofluoress under
both wavelengths. The autoflorescence is there regardless of the fixative
and the antibodies used (I have done all the tests).
Is there a way of quenching or blocking this autofluorescence before doing
the immuno?
Thanking you in advance for your help,
Lilith
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Lilith Ohannessian-Barry
National Research Council
Institute of Biological Sciences
CANADA
Tel;613-993-6460
Fax;613-941-4475
e-mail; lilith.barry@nrc.ca